Molecular beam chemiluminescence. Collisional dissociation of tetramethyldioxetane by a fast xenon beam

The chemiluminescence arising from collisional dissociation of tetramethyldioxetane (TMD) by a supersonic xenon beam is recorded as function of collision energy (1–4.6 eV) and of TMD pressure. At TMD pressures as low as 5 × 10^?5 torr a third-order process is prominent, demonstrating the importance of secondary collisions which enhance the light yield. The energy dependence shows a threshold at E_O ≈ 30 ± 3 kcal/mol. Structure in the energy dependence is interpreted in terms of a rise with energy of the singlet/triplet acetone branching ratio.